Minimum castor content?

I have read from Jim Wade's record setting Eagle II proto speed article that he considered 4% castor oil to be the the minimum required to keep the ball-socket joint in tact. On my 65% nitro contest fuel, I find 5% castor and 15% synthetic oil seem to work well as a blend. So to answer your question, if you can end up with about 5% castor oil in your fuel with an overall oil content of 20-25%, you ought to be fine. Good luck!

Cheers, Paul

Paulgibeault wrote:I have read from Jim Wade's record setting Eagle II proto speed article that he considered 4% castor oil to be the the minimum required to keep the ball-socket joint in tact. On my 65% nitro contest fuel, I find 5% castor and 15% synthetic oil seem to work well as a blend. So to answer your question, if you can end up with about 5% castor oil in your fuel with an overall oil content of 20-25%, you ought to be fine. Good luck! Cheers, Paul

This is good news, Paul. I have heard all sorts of numbers and one would never know what is correct. Never heard any numbers as far as how much Castor to go with. This then definitely eliminates the modern RC 2% Castor with 16% Synth oil blends. The 10%/10% blend of Cox Champion definitely fits in.

For those who must resort to the 18% mostly Synth stuff then can at least have some assurance when they add Castor to bring it up to standards, which is easily then achievable.

Wildcat 15% Nitro Aircraft Fuel (16% oil content, 80% Synth/20% Castor):

Fuel Item	Percent	Ounces
Nitro	15.0	19.2
Synth Oil	12.8	16.4
Castor Oil	3.2	4.1
Methanol	69.0	88.3
Total	100.0	128.0

Omega with 6.5 ounces Castor Oil Added:

Fuel Item	Percent	Ounces
Nitro	14.3	19.2
Synth Oil	12.2	16.4
Castor Oil	3.0	4.1
Castor Added	4.8	6.5
Methanol	65.7	88.3
Total	100.0	134.5

Omega New Fuel Oil Content:

Oil	Percent	Ounces
Castor	7.9	7.9
Synth	12.2	16.4
Total	20.1	24.3

Omega New Fuel Oil Relationship:

Oil	Percent
Castor	39.27
Synth	60.73
Total	100.00

I managed to get 3-4 quarts of buggy fuel at 1/2 price at a local toy store sale.  It has 16% nitro and I contacted the manufacturer and they claim 18% oil with some caster, but wouldn't tell me the blend.  I used this great calculator to bring the blend up to 25% nitro & 25% oil, so I figure I've got plenty of caster even though I don't know the exact percentage.  It seems to work great.

I do wonder if we may have been a little hasty insisting that Hobbico make the Cox fuel full caster.  As Paul has pointed out, through probably more experience than any of us, full caster isn't necessary and I believe there may be some benefits to having a certain amount of synth.

Rod.

Oldenginerod wrote:I managed to get 3-4 quarts of buggy fuel at 1/2 price at a local toy store sale.  It has 16% nitro and I contacted the manufacturer and they claim 18% oil with some caster, but wouldn't tell me the blend.  I used this great calculator to bring the blend up to 25% nitro & 25% oil, so I figure I've got plenty of caster even though I don't know the exact percentage.  It seems to work great.

That is good, Rod that you had that. I didn't, so I used a spreadsheet to figure out all the values.

I do wonder if we may have been a little hasty insisting that Hobbico make the Cox fuel full caster.  As Paul has pointed out, through probably more experience than any of us, full caster isn't necessary and I believe there may be some benefits to having a certain amount of synth. Rod.

I don't think so, Rod. The 10% Synth + 10% Castor for 20% total Hobbico is making the new fuel to be is conservative and definitely within a safe range. Sig has been marketing theirs for a long while, and remains a standard for commercially available half-A fuels. Problem is previously the Cox fuel was inadequate at around 1% Castor, (can't recalled exact number, I ran the calculations and would need to redo again), which was definitely under par.

For a newbie who accidently sets his engine excessively lean, or a flier who crashed, wiped off the grass and dust, washed quickly in fuel to refly again, only to have the engine go excessively lean, or overpropped it by chance, the RC'er stretching his flight was a really hot running engine at extended lengths, this new fuel mix may be granted a chance they didn't ruin their engine for good, and be able to fly another day.

Anyway, that is my take on the situation.

GallopingGhostler wrote: The 10% Synth + 10% Castor for 20% total Hobbico is making the new fuel to be is conservative and definitely within a safe range.

Sorry George, my mistake. I was under the impression that the new blend was 20% full caster oil, rather than 10%/10%. Should have done my homework.

Rod.

I have an unopened quart of 30% (Nitro) Buggy fuel that I got from Tower Hobbies quite some time ago. Since becoming a member here at CEF, I have learned that it's a good thing that I never used it in any of my engines. My Cox engines have only been run on the old original Cox Super-fuel/racing-fuel and Sig Champion 1/2A 25/35.. period.

The quart of Tower 30% would only (and only possibly..) be suited for my OS .10FP engine.. but the fuel's oil content is not listed on the bottle.. so I wouldn't try it before doing some research.

As for my old iron piston/sleeve engines... I haven't really run any of those at all. It's been at least 25 years and likely as many as 40 years (for most of them) since they have been run. It's been recommended that I obtain a fuel like "Powermaster" 10/20 for these engines. I assume this blend to be 10% nitro and 20% total oil (50% synth./50% Castor). So.. a 10/22-blend would be 10% nitro and 22% total oil (50% synth./50% castor).. is this the correct break-down of the formulas?

There is and always will be a castor oil debate.

For my diesel engines, it is castor only - running in 30%, run in 25%, ball race 20% - tuned for speed - 15%. The reduction in castor is replaced with paraffin (kerosene) to provided more power. I have a book, published in 1947, that has a chapter devoted to model diesel fuels some of the mixes (80% ether) using motor car engine oil look horrendous to me but they seemed OK at the time.

With glow engines the problem arises if you run too lean or over heat. Castor oil provided a degree of protection against this that the synthetic fuels cannot. While it may be stated that a modern 2 stroke glow is happier running on synthetic oil, much cleaner and a better lubricant, allowing the engine to run lean and/or overheat will result in catastrophe. I know some who add a touch of castor oil as "insurance" but then regret ending up with a gummy engine, reduced performance and the inevitable dirty exhaust.

From the forum here, there is definitely consensus that the Cox engines with the ball socket piston benefit from castor oil. All recommendations point to around 20% oil, albeit a mixture of castor and synthetic. Suggestions on the make up is from 5% castor/15% synthetic to 20% castor.

I have no doubt that for speed models lowering the castor content is beneficial but how important is engine life expectancy. Cylinder/pistons for Cox 049s are relatively cheap. If you only want an engine to last minutes in competition - Why worry?

If the engine is your pride and joy and you want hours out of it - err on all castor side. Although, I have seen 049s with little wear that have been run on 8%/12% and 10%/10% mixes. In each case though - the engine was not leaned out to the nth degree!

As an anecdote, my old 1970s mini needed an oil change every 3,000 miles with a top up every 500 miles. My current mini only needs oil changes every 15,000 miles and in 81,000 miles has never required topping up! Mind you! I don't remember going ouch when buying oil for the old mini but modern super duper synthetics are a little more than ouch on the expense side.

We can debate oils for model engines for ever but just remember to take care not to run too lean and allow the engine to overheat - even if you use castor!

I just figured that going from 18% to 25% oil by adding caster would easily give me enough caster for most general sport flying.  If the fuel I had was 18% oil, including some caster, I would assume it would use at least 2% caster.  With the caster I added to bring it up to 25%, I'm confident the caster content will be quite adequate considering that Paul seems happy with 5% caster for his engines.
Roddie.  I can't imagine any buggy fuel having more than about 15%-18% oil, so if you can't find the actual oil content from the manufacturer, just assume it's on the lower side and add enough caster to bring it up to 25%.  That should still give you more than enough.  Sure, you won't know exactly what your percentages are (the added oil will bring down the nitro %) but if optimal performance is not on the agenda, the fuel could still be quite useful to you (and safe).  Try the calculator in my previous post.  It's really nifty & simple.

Just checked.  Some of the car/boat fuels that Tower sell are as low as 10% oil.  You won't overdose on oil even if you assume it's 10% & add another 15%.  Diesels generaly run 33% caster.

Thanks Rod. I've never purchased castor alone for formulation.. or any of the other fuel components separately. Custom-blending fuel would be new for me.. so until I start running engines on a regular basis, I'll stick with the tried and true pre-blends.

Thanks everyone!

That IS a cool calculator Rod. Wish it would do metric though, I am illiterate when it comes to fluid ounces... I can do gallons and quarts (and a few pints every now and then ), but these smaller units get me confused. Never seem to remember how many ounces there is in a quart and so on.

Anyway, I did some calculations with pen and paper and ended up with one potential solution: If I add to my one litre (1000cc) of fuel 170cc of castor and 180cc of pure nitro I'll end up with 1.35 litres of fuel blend which contains:

52% Methanol
20% Nitro
15% Synthetic oil
13% Castor oil.

This is just one example, I think I'll shoot for a little less nitro and castor to keep the total lube content at around 25%. And I won't mix the whole batch at once either, I'll get some 100 or 200cc bottles and big syringes for measuring the components.

I will try the mix on one of my late model Babe Bees, in the worst case I will destroy the small end of the con rod, but one has to make sacrifices in the name of science, right?

EDIT:
Re-calculated with 100cc of additional castor and the same amount of additional nitro =>
58,3% Methanol
16,7% Nitro
16,7% Synthetic
8,3% Castor

I guess I could shoot for a total 10% of castor by adding it just a little more. According to the manual, the minimum requirement is 20% lube, minimum 50% of it castor. So, my fuel would contain 10% castor and maybe 15-16% of synth, the extra 5-6% of synth shouldn't hurt, right? On the other hand, if Paul with all his experience states that 5% is enough, I believe it. We'll see what happens after I get my fuel lab and engines sorted out

Just curious, have any of you tried Byron Prem 1/2A full castor? It's the easiest fuel to get on short notice where i'm at and have had pretty good luck with it so just wondering. (Bandit)

TDbandit wrote:Just curious, have any of you tried Byron Prem 1/2A full castor? It's the easiest fuel to get on short notice where i'm at and have had pretty good luck with it so just wondering. (Bandit)

Never used that Byron, but I used to fly with 100% Castor oil. That was what was avaiable in the 1970's. Only thing is after a while, I diassembled my Coxes due to varnish build up, soaked in solvent, then proceeded to use fine steel wool to remove the varnish build up off cylinder walls and piston; after reset piston con rod socket. That restored RPM.

TDbandit wrote:Just curious, have any of you tried Byron Prem 1/2A full castor? It's the easiest fuel to get on short notice where i'm at and have had pretty good luck with it so just wondering. (Bandit)

I haven't used it and I see nothing wrong with running full castor. If anything you will just have to devarnish more often.

I wouldn't hesitate to use full castor if that's what was available in my area.

Ron

TDbandit wrote:Just curious, have any of you tried Byron Prem 1/2A full castor? It's the easiest fuel to get on short notice where i'm at and have had pretty good luck with it so just wondering. (Bandit)

I haven't searched extensively but the mail order places and web sites I have found in Finland so far seem to have fuel mixes with synthetic only. Fortunately all the "components" are available separately, although for nitro you need a licence from the police. Shouldn't be a problem for me to get one, I haven't been in trouble, unless speeding tickets count

And, the smallest quantity of pure methanol available is a 5 litre jug, that makes about 8 litres of fuel, equals to 1000 full tanks for a Golden Bee. Takes me years to burn that amount.

Do not worry Kari about the 8 liters of fuel...., I have burnt plenty of fuel in my 010-s, 020-s, 049-s, 050-s and 051-s since 2010 when I restarted modeling. My garage is already full with empty 5 liter FAI fuel cans..you will not even notice how fast time flies when running COX stuff...

KariFS wrote:Thanks everyone!

That IS a cool calculator Rod. Wish it would do metric though, I am illiterate when it comes to fluid ounces...

Calculator works exactly the same for metric. If you're working with 1 litre, just punch in 1,000 ounces. Whatever ounces the calculator tells you to add, just add that many millilitres (CCs).

Supporting Paul's comments, I found this post in:

https://www.coxengineforum.com/t5113p60-hobbico-s-cox-super-fuel#88589

Cox International wrote:There have been extensive tests performed with various castor / synthetic oil mixes and although, under some ideal circumstances, one could use as little as 25% castor / 75% synthetic mix, the consensus is that a 50% castor / 50% synthetic mix or better should be used to prevent engine damage.

This is due to the unique nature of Cox engines, with no piston rings, OEM tolerances of 2 /1,000,000” on cylinder / piston fit and Cox’s unique ball and socket joint for the piston / conrod assembly. Basically, Cox engines were engineered to require castor oil and no synthetic oil currently available (that we are aware of) would be a good substitute for castor oil. (quote from Bernie)

Paul, I gather that you're unique in that you are a seasoned veteran competitor, where you know how to extract the last drop of power out of these little .049 jewels of engines.

Thus for those know exactly what they are doing, can go with a lesser amount, the 5% Castor and 15% synth for 20% total (oil added is 25% Castor and 75% synth). I appreciate that info as it substantiates my adding 6 oz. Castor to a gallon jug of RC fuel, which roughly ups the oil to 22% total with 6% as Castor (from the 18% oil total with 2% Castor as manufactured) would not damage my engines if I excercise care.

Overall, since a good number including me don't always exercise utmost caution and care for our half-A's, (who hasn't had a lean run or crash, brushed off the grass, refueled and ran lean?), I gather / sense most the sport flying community are better off following the general consensus of 20% oil total with 10% Castor mininum and 10% synth.

This is interesting stuff, to say nonetheless. The good part is, if one of us happens to short live a .049 Cox engine, parts are available to restore it to good running order.